A touch panel including an input unit (pointing device) has been extensively used in displays of electronic devices such as personal digital assistants (PDA), a notebook computer, office automation (OA) device, a medical device, or an automobile navigation system. For example, a capacitive type touch panel is generally known in the art as well as a resistive type touch panel, an electromagnetic induction type touch panel, and an optical type touch panel.
In general, the capacitive type touch panel is classified into an analog type and a digital type.
Since the analog type touch panel includes a sheet type sensor electrode, a pattern is not required on a sensing region. However, the digital type touch panel requires a pattern for a sensor electrode in the sensing region. The digital type capacitive touch panel induces a current to confirm a touch location based on variation in capacitance caused by electrostatics of a human body and a transparent electrode. For example, in order to detect a location in the touch panel touched by a finger or a stylus, various technologies for the capacitive type touch panel have been developed.
For example, a lattice touch-sensing system for detecting a position of a touch on a touch-sensitive surface is disclosed in U.S. Pat. No. 6,970,160. The lattice touch-sensing system may include two capacitive sensing layers separated by an insulating material where each layer consists of substantially parallel conducting elements, and the conducting elements of the two sensing layers are substantially orthogonal to each other. Each element may be prepared as a series of diamond shaped patches that are connected together with narrow conductive rectangular strips. Each conducting element of a given sensing layer is electrically connected at one or both end portions thereof to a lead line of a corresponding set of lead lines. A control circuit may also be included to provide an excitation signal to both sets of conducting elements through the corresponding sets of lead lines to receive sensing signals generated by sensor elements when a touch on the surface occurs, and to determine a position of the touch based on the position of the affected bars in each layer.
The capacitive type touch panel generally includes two capacitive sensing layers. The two capacitive sensing layers are spaced apart from each other while interposing an insulation material therebetween in order to generate a capacitive effect between the two layers. Such a structure significantly increases a thickness of a structure of a panel which results in adversary effect on the miniaturization. Further, the capacitive type touch panel according to the related art includes a substrate on both surfaces thereof on which the two capacitive sensing layers are formed, respectively. Therefore, through holes must be formed in the substrate to serve as vias and circuit layering must be adopted in order to suitably connect conductor elements of the sensing layers to each other. Thus, the manufacture of the capacitive type touch panel may become difficult and complicated.
Accordingly, in order to solve the above problem, a scheme of reducing two capacitive sensing layers to one capacitive sensing layer has been used. Recently, a scheme of configuring sensing layers (sensing electrode pattern layer) as one layer and connecting the sensing layers to each other through a metal bridge has been used.
FIGS. 1 and 2 are sectional views illustrating a touch panel according to the related art, which shows a section of a metal bridge of the touch panel for connecting the sensing layers (sensing electrode layers) to each other.
The touch panel according to the related art will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, a metallic or non-metallic material 140 for forming a metal bridge is formed on a transparent window 110, and a photoresist 155 is formed on the metallic or non-metallic material 140 to etch the metallic or non-metallic material 140.
Next, as shown in FIG. 2, the metal bridge 150 is formed through an etch process.
In this manner, if the metallic or non-metallic material 140 is etched, since the end portion of the metal bridge 150 generally has no vertical structure, the metal bridge 150 has a trapezoidal shape, a reversed trapezoidal shape, a concave shape, or a convex shape. The above shape may be caused due to under cut when the material 140 has a single layered structure and due to a difference in etching rate between metals forming respective layers when the material 140 has a multi-layered structure.
According to the related art, since step difference L occurs in an end portion of the metal bridge 150 so that an angle between the end portion of the metal bridge 150 and a transparent window reaches at least 70°, external light is reflected by the metal bridge 150 so that the visibility of the touch panel is degraded.